1. Field of the Invention
This invention relates to casein coatings for leather applied as aqueous systems.
2. Description of the Prior Art
Leather finishes have employed casein to improve the "hand" of the leather as well as optical properties, such as color and gloss. Grained leather, in particular, requires the application of a surface finish coating to provide gloss. Generally, aqueous systems are utilized to apply the casein finish to the leather. Without further treatment, casein coatings remain sensitive to water, tending to dissolve or swell when exposed to water. Generally, casein coatings for leather have been cross-linked or cured so as to reduce the water sensitivity of the coating. Formaldehyde or glutaraldehyde has been used in the prior art to cross-link or cure the casein. Alternatively, melamine ethers have been used to cure the casein.
The drawbacks of the utilization of formaldehyde to cure casein coatings for leather are well known. Because of the high volatility of formaldehyde, its use as a cross-linking or curing agent for casein is disadvantageous from a toxicological standpoint. The use of glutaraldehyde as a cross-linking or curing agent is also disadvantageous since glutaraldehyde cross-linked casein finishes for leather tend to discolor with age. A representative prior art process for finishing leather with casein is disclosed in Swiss Pat. No. 271,085.
It is therefore an object of this invention to provide a process for finishing leather utilizing casein which avoids the disadvantages of formaldehyde or glutaraldehyde as cross-linking agents to reduce the water sensitivity of the casein coating.